A number of technologies, which, even when a tire goes flat while a vehicle is traveling therewith, makes an emergency run possible for about several hundred kilometers, have been proposed. As a representative example thereof, there is a proposal of a tire/wheel assembly (tired wheel) which makes run-flat traveling possible in a manner that, with a core being mounted as a run-flat support member on a rim inside a cavity portion of a pneumatic tire assembled onto the rim, the pneumatic tire in a deflated condition is supported by the run-flat support member (refer to Patent Documents 1, 2 and the like).
The run-flat support member of this tire/wheel assembly is configured by attaching elastic rings, which is formed of hard rubber or the like, to sides facing inner diameters of legs of an annular shell having an arched cross-section, and has an advantage that it can be used with the configuration as it is, without adding substantial modifications to an existing wheel-rim configuration.
Incidentally, the run-flat support member as described above, which includes as a main constituent member, the annular shell having an arched cross-section, is manufactured by forming a cylindrical body formed of a metal sheet into the annular shell through a drawing process in a manner that the cylindrical body is pressed with forming dies (rollers) both from an outer periphery and from an inner periphery thereof while the cylindrical body is rotated.
The thus manufactured run-flat support member can be more enhanced in run-flat durability if a metal material used thereof is higher in breaking strength. However, the higher in breaking strength the metal material is, the more difficult it is to form the material through a drawing process. Because stresses concentrate particularly on inner ends of the two legs of the arched cross-section, there has been a problem that wrinkles, cracks and the like are generated.
Consequently, in the case where the abovementioned run-flat support member constituted of the annular shell is obtained by the drawing process, there is a conflicting relationship between the enhancement in run-flat durability of the run-flat support member and the enhancement of formability (productivity) without generating wrinkles and cracks. Hence, compatible achievement of these issues has been an important problem.                [Patent Document 1] Japanese patent application Kokai publication No. Hei 10-297226        [Patent Document 2] Japanese patent application Kokai publication No. 2001-163020        